This invention relates to traffic signals for controlling traffic flow at intersections of roadways, and relates more particularly to systems and devices that modify traffic signal operation in response to preemptive emergency vehicle signals to permit the emergency vehicle to pass quickly and safely through the intersection, and to methods of controlling such signals.
Traffic signals have been used for many years to regulate traffic flow at intersections, typically providing a green or “go” light for traffic on one street at preselected intervals while providing traffic on the intersecting street with a red or “stop” light. During the transition from “go” to “stop”, it is customary to provide a yellow or “caution” light for a short interval, warning oncoming motorists to prepare to stop when the red light appears. All three lights often are mounted in a common housing or frame, usually in a vertical row but sometimes horizontally aligned.
When an emergency vehicle such as a police car, fire truck or ambulance must pass rapidly through an intersection, the oncoming emergency vehicle typically sounds an audible warning such as a siren and a visual warning such as a flashing light, and then proceeds through the intersection without regard to the existing condition of the traffic signal. For various reasons, these signals are not always sufficient to avoid collisions. Loud noises, closed vehicles with radios or other audio devices playing, and inattentive drivers in some instances lead to dangerous situations in which cross traffic does not stop for the oncoming emergency vehicle, with resulting collisions.
A variety of methods, systems and devices have been proposed to allow emergency vehicles to control traffic signals. These typically use radio transmitter systems for activating emergency preemption controls on the traffic signals that will override the normal controls of the signals and provide “stop” signals for cross traffic approaching the intersection and continuous “go” signals for the emergency vehicle. Other special signals have been provided in efforts to provide information to affected drivers regarding the presence and direction of approach of emergency vehicles, whether on intersecting streets or from one direction or the other on the same street. Such systems and devices are well known, and examples are shown in U.S. Pat. Nos. 4,775,865 and 4,704,610 (signs beside traffic signals with vehicle symbols for indicating approaching emergency vehicles); U.S. Pat. No. 6,292,109 (display at comer of intersection with sign shown in FIG. 6 having arrows indicating the direction of an approaching vehicle, a traffic signal with a siren and a flashing red emergency light); and 6,362,749 (signal device installed in vehicles and having arrows for indicating the direction of the signal from an approaching emergency vehicle, which also could be installed in an undisclosed manner on a traffic signal).
Unfortunately, these prior devices, systems and methods have provided ambiguous and sometimes confusing information and often have been so complex and expensive in construction that they have not been universally installed. Others have been unreliable in operation and have required substantial time and money for maintenance. Accordingly, there has been an ongoing need for an improved and more effective emergency traffic signal device and method that will overcome the deficiencies of the prior art systems and devices.